Autopsies of soldiers killed by mustard gas in World War I indicated that sulfur mustard has a disproportionate effect on rapidly dividing cells and suggested that sulfur mustard compounds might have antitumor effects. Indeed, early researchers attempted to treat cancer by direct injection of sulfur mustard into tumors. This research was limited by the extreme toxicity of sulfur mustard compounds and nitrogen mustard analogs, such as mechlorethamine, were investigated as less toxic alternatives.

Because of the lack of selectivity of most mechlorethamine analogs, prodrugs, such as phosphoramide compounds, which can be activated by the high concentration of phosphoramidases present in neoplastic cells, have been investigated. Two phosphoramide alkylating agents, cyclophosphamide (CPA) and the isomeric compound Ifosfamide (Ifos) have proved to be particularly effective.

With reference to FIG. 1, isophosphoramide mustard (IPM) is a common metabolite of CPA and Ifos. IPM is thought to be responsible for at least a portion of the anti-tumor activity exhibited by CPA and Ifos. Efforts to use IPM as an anticancer agent directly have been unsuccessful due in part to the compound's instability. IPM has been synthesized and preliminary biological evaluations of the compound have been conducted, but unfortunately IPM is too unstable to be isolated and used for human treatment.